Zika virus: who is at risk, is there a vaccine, how does it spread and more ()

The Zika virus can cause serious birth defects if a pregnant woman is infected, the USA's Centers for Disease Control and Prevention has confirmed.

Following its spread to South America after a 2014 outbreak in French Polynesia, Zika has been declared a Public Health Emergency of International Concern by the World Health Organisation earlier this year. The virus is pri fmarily spread by the Aedes mosquito and is related to dengue fever.

The effects and symptoms of Zika virus can vary widely from person to person. In most people, the virus causes a mild disease lasting between two and seven days, with key symptoms including fever, rash, aches, conjunctivitis and eye pain.

However, in a minority of people, Zika has been found to cause Guillain-Barré syndrome, an auto-immune disease which makes the immune system attack the body's nerve cells, resulting in weakness of the muscles and even paralysis. The effects typically last between a few weeks and a few months, but are sometimes permanent. Other neurological and autoimmune diseases, including acute disseminated encephalomyelitis, have also been linked to Zika.

The most notorious effect of the virus is its now-confirmed ability to cause foetal abnormalities if a pregnant woman contracts it. Following a study published by The New England Journal of Medicine, Dr Tom Frieden, director of the US Centers for Disease Control and Prevention, said that "it is now clear that the virus causes microcephaly." Microcephaly prevents the brain from developing during gestation, resulting in abnormally small head and brain sizes, frequently resulting in the death of the infant upon birth and causing severe physical and intellectual disability in those which survive.

Pregnant women and those who are likely to conceive are at risk of suffering birth defects, although the CDC notes that "some infected women have delivered babies that appear to be healthy."

Those at risk of neurological diseases such as Guillain-Barré are harder to identify, as no particular increased risk has yet been associated with people of a particular age or group. However, in areas where Zika is endemic, it's important to ensure that children, the sick and the infirm are properly protected against mosquito bites, as they may be less able to take precautionary measures of their own.

The primarily infection vector for Zika virus is the Aedes mosquito, which also spreads the related dengue virus.

Zika can also be transmitted from mother to child during pregnancy, and can also be transmitted sexually, particularly through semen. The WHO says that, so far, "sexual transmission of Zika virus has been described in 2 cases, and the presence of the Zika virus in semen in 1 additional case."

Blood transfusions are also a potential source of infection. The CDC reports that "during the French Polynesian outbreak, 2.8 per cent of blood donors tested positive for Zika and in previous outbreaks, the virus has been found in blood donors."

Public Health England reports that Zika virus is currently active in multiple countries in the Caribbean, Central and South America, the Pacific Islands and parts of Asia.

Jeremy Farrar, an expert on infectious diseases warns that "it's spread across a whole continent and it's likely to invade the United States. Then it's highly likely to spread around the world and we have no method to control it."

In regions were Zika is endemic, it's important to avoid being bitten by mosquitoes. Mosquitoes are attracted to stagnant pools, puddles and buckets of water. Individuals in affected regions are advised by the WHO to routinely clean, cover or empty water containers, to wear light-coloured clothes that cover as much of the body as possible, to use physical barriers and mosquito nets to keep the insects away, and to use appropriate repellents and insecticides, which should contain DEET, IR3535 or icaridin.

Mosquito avoidance is also important for those who have already contracted the disease. The Pasteur Institute notes that "symptoms appear three to 12 days after the bite but, during this time, the person can infect other mosquitoes if they are bitten again. This is why people suffering from Zika must avoid getting bitten to break the viral transmission cycle."

If infected, you're advised to treat the virus by ensuring that you get plenty of rest and fluids and using over-the-counter medicines such as paracetamol to reduce fever symptoms. Should your condition worsen, you're advised to seek medical care.

Women in many areas affected by Zika including Jamaica, Brazil, Colombia and El Salvador have been advised to avoid becoming pregnant for the duration of the outbreak. Condoms and other barrier methods of birth control can also prevent transmission from one partner to another through semen. While non-barrier methods don't protect women from the sexual transmission of Zika, they will effectively prevent conception.

UK government travel advice notes that "women should be advised on the potential risks of Zika virus infection in pregnancy. It is recommended that women should avoid becoming pregnant while travelling in an area with active Zika virus transmission, and for 28 days after their return. This allows for a maximum 2-week incubation period (the time between exposure to an infection and the appearance of the first symptoms) and a possible 2-week viraemia (presence of virus in the bloodstream). Following this, attempts to conceive can resume"

There is currently no vaccine for Zika.

Dr Anthony Fauci of the USA's National Institute of Allergy and Infectious Diseases told the BBC that initial trials of a Zika vaccine would start in September this year, with larger trials potentially beginning as early as 2017. This means that a best case scenario would see a Zika vaccine developed by early 2018. However, much of this is dependent on the US Congress granting a request for $1.9 billion in funds to work against the virus.

Another two Zika vaccines are currently in development by India's Bharat Biotech, with pre-clinical trials due to be concluded in the coming months. Dr. Krishna Ella told The Hindu that "at the time we started working on the Zika vaccine, there was not a market incentive or any demand for it- largely because the symptoms are mild. But we were already working in chikungunya and our hypothesis was that the same vector transmits this disease as well, so we thought we need to look at this aspect as well."